Selective binding of chiral molecules of cinchona alkaloid by β- and γ-cyclodextrins and organoselenium-bridged bis(β-cyclodextrin)s

The inclusion complexation behavior of chiral members of cinchona alkaloid with β- and γ-cyclodextrins (1 and 2) and 6,6′-trimethylenediseleno-bridged bis(β-cyclodextrin) (3) was assessed by means of fluorescence and 2D-NMR spectroscopy. The spectrofluorometric titrations have been performed in aqueous buffer solution (pH 7.20) at 25.0 °C to determine the stability constants of the inclusion complexation of 1–3 with guest molecules (i.e., cinchonine, cinchonidine, quinine, and quinidine) in order to quantitatively investigate the molecular selective binding ability. The stability constants of the resulting complexes of 2 with guest molecules are larger than that of 1. As a result of cooperative binding, the stability constants of inclusion complexation of dimeric β-cyclodextrin 3 with cinchonidine and cinchonine are higher than that of parent 1 by factor of 4.5 and 2.4, respectively. These results are discussed from the viewpoint of the size-fit and geometric complementary relationship between the host and guest.